CALL IT an exceptional case, but the Dec. 7 crash of Pacific Southwest Airlines Flight 1771 in the mountains of California -- which killed all 38 passengers and five crew members -- was reason enough for the latest tightening of security rules for all airline and airport employees. Investigators believe that a fired USAir employee smuggled a weapon aboard the jet and opened fire during flight; they also believe that the former employee used his familiarity with former co-workers and possibly an uncollected security badge to avoid a screening checkpoint. The new rule calls for all airline and airport employees -- including uniformed flight crews -- to pass through those checkpoints. Another measure under consideration would require better tracking systems for those badges. These moves make sense -- and should be vigorously enforced.

No one enjoys the prospect of further inconveniences, and the negative response of the Air Line Pilots Association is no great surprise. Organization officials promptly labeled the security-check rule "an overreaction" -- a term that might better describe their own statement. "If you think delays and passenger missed connections are bad now," said ALPA President Henry Duffy, "see what happens if we clog the checkpoints with thousands of pilots, flight attendants and other airline and airport employees. The association has suggested that the Federal Aviation Administration issue computerized cards with individual coded numbers that would allow employees access through locked doors to secure areas. Fine. Whenever that system is ready, it should help -- but why wait for that?

Quite aside from this month's crash, General Accounting Office investigators have reported at a congressional hearing that thousands of airline and airport employee ID cards cannot be accounted for at major airports around the country. While conducting security surveys at six airports, these investigators were able to roam freely through restricted areas without challenge. GAO investigator Kenneth Mead testified that "without wearing identification, we entered open or unlocked cargo doors, walked through the buildings or gates and out onto the air operations area and had access to cargo shipments or aircraft. We gained easy access to restricted areas while attired in clothing similar to that worn by one airline's flight attendants."

The new rules, along with more measures to match bags with passengers actually on board, will no doubt cause some inconveniences. But then so do all those other rites that take place before takeoff, including the pilot/copilot checklists and the little things that passengers are told to remember in case of trouble once aloft. What happens on the ground before takeoff can spell the difference between life and death for everybody in the air.